Drayton wiser system overriding the boiler temperature “set point”

fatrascal1979

Novice Member
Hi. I have had the Drayton Wiser set up for a couple of years now. I like it, and think it’s a really smart system. HOWEVER…!! Every so often, the boiler’s temperature set point reverts back to 45 degrees.

When the radiators are calling for heat, the message “Set point 45 degrees controlled by room stat” scrolls across the display on the boiler. This means that none of the radiators calling for heat get anywhere near hot enough to warm the rooms.

To resolve this, I have to switch the boiler off and switch back on again. Clearly this is not a practical solution.

Has anyone else had this problem or understand what is going on?

This never happened before wiser was installed. I have called their support desk, and I’m struggling to get anywhere with them.
 

Deezell

Active Member
When you say radiators are calling for heat, I assume you have smart TRVs fitted to the rads. Do you also have a Drayton wall thermostat in the system measuring room temperature. Is the Drayton Hub receiver wired to the boiler using the OpenTherm digital connection, or does it just power the boiler on and off. The vast majority of CH system thermostats operate the boiler in On/Off mode, a simple relay switch opens and closes when the the stat reaches target temperature or fall below it. The room stat or Smart TRV has no mechanism to know or control the setpoint temperature of the boiler. Thermostat closes, boiler fires, heated water is pumped to the rads, boiler water temperature will rise towards its set point depending on how cold the rooms are and how many rads are on. It might not reach its setpoint even, but when it does, the boiler will cut, and cycle, on off, as long as there is heat demand from a closed thermostat relay.

Now, if you have a thermostat calling the boiler via OpenTherm digital two wire connection, the thermostat can regulate the static boiler temperature. As the room temperature reaches the target set on the stat, the stat will communicate this to the boiler, which will reduce the jacket water temperature down such that it will maintain room temperature set on the stat with a constant flow of less hot water, rather than with a series of on off bursts of higher temperature water which is the norm with simple on off relay controlled boilers. Some smart stats like Tado can simulate the boilers own temperature control by modulating the on off periods of the stat relay as it approaches set temperature, effectively 'modulating' the boiler to cool the flow output temperature, and thus increase condenser boiler efficiency. This is only practical in a system where a single stat is controlling the boiler.

With smart TRVs, there are multiple sources calling for heat, so the boiler can really only operate at setpoint, and each radiator draws and reduces this hot flow as it's TRV approaches target, whence it closes completely and stops calling the boiler. Again, some smart TRVs will squeeze the flow and modulate the calls to the boiler to try and maintain a continuous less hot flow to maintain room target temperature.
It's possible that you have the Drayton hub wired to the boiler in OT mode, but this would only work if the wall stat is the only source of a boiler call from the hub. If there are Drayton smart TRVs calling the boiler via the hub, and maybe a Drayton wall stat also paired to it, its possible that there is a conflict in that the hub instructs the boiler via a digital OT connection to modulate its setpoint down to 45, which maintaind the target temperature of the wall stat. Meantime a smart TRV opens, and it requires the boiler to open up fully to a high setpoint to get the rad up and running, but the modulated request from the overriding wall stat is preventing this.

Thats a theoretical scenario. You may not have an OT connected hub at all. The boiler may have a dodgy boatrd or fault whereby it thinks it's getting temperature setting information from a stat. (it must be capable of connection of such a stat, either by OT digital or its own built in optional wireless receiver, as it can scroll the message you describe). Perhaps when you got the wiser connected, you did not remove or disable the boilers existing proprietary wireless thermostat receiver, and it's still trying to control the boiler, hence the message. This is the most likely cause, as you've had the Drayton a few years, its unlikely you got a hub with OT terminals, and assuming your boiler had an existing wall stat, it may well still be in place, and conflicting with the simple on off requests from the Drayton hub receiver.
 

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